The present invention relates to a method of preparing superabsorbent synthetic fibers wherein individual synthetic fibers are coated with a water-soluble polymer which is rendered water insoluble during complexing in situ.
Superabsorbent systems are known in the art. Superabsorbent materials are water insoluble, water swellable compositions of matter which have the capacity to absorb many times their weight in water.
In the prior art known at this time, U.S. Pat. No. 4,090,013 teaches making superabsorbent ionic complexes but does not teach how to coat the resultant polymer onto a substrate. U.S. Pat. No. 4,128,692 discloses precipitating already covalently crosslinked absorbents onto cellulose fibers from an aqueous slurry followed by solvent dehydration. U.S. Pat. No. 4,310,593 teaches the preparation of superabsorbent films and fibers from anionic polyelectrolytes which are crosslinked covalently with an amine/epihalohydrin adduct. The patent also suggests that synthetic and natural fibrous substrates (such as wood pulp) may be coated with said superabsorbent composition.
A need remains, however, to find processes for making superabsorbent fibers that are less complex, less expensive and safer than the processes taught by prior art. The present invention fulfills these needs. Moreover, the process of the present invention has broad application to a large number of synthetic fibers.
Most superabsorbent compositions are sold in powder form for use in products such as absorbent dressings, diapers, tampons, and the like. Superabsorbent particles or powders are difficult to use because they do not remain stationary during the manufacturing process and often change position before the product is completed. Further, superabsorbent powders have the disadvantage of easily absorbing on their extended surface area any water that is present in the production process. The powders will swell and it is very difficult to dry the swelled powders in the finished article. Such articles are thus more difficult and expensive to make because of the additional processing necessary to make them. The difficulty of placing and maintaining the superabsorbent on a substrate has been addressed in many ways: by making webs in which the superabsorbents are placed, by bonding, and by other techniques.
The discrete coated synthetic fibers of the present invention provide an improved solution to these problems. They are easy to use, especially when they are air laid or dry laid in non-woven fabrication processes. The coated fibers can also be mixed with other absorbent materials for use in converted products; one example is as an addition to cellulose fluff pulps for use in diapers. The coated synthetic fibers of the invention can also be incorporated into non-woven card and bind webs or used in melt-blown and other non-woven products, which are typically not hydrophilic, without causing a reduction in strength.
The coated synthetic fibers of the invention are easily used in varying woven and non-woven products, staying more easily in place than absorbent powders and, moreover, have the tremendous range of properties which are related to the particular fiber which forms the base for the superabsorbent polymeric coating. Thus, for example, it is possible to make polyethylene or polypropylene products which are also superabsorbent.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.